An instrument that measures earthquake magnitude is called a seismometer or seismograph. These devices detect and record the vibrations produced by seismic waves during an earthquake. The data collected by seismometers are used to calculate the earthquake's magnitude on the Richter scale or the Moment Magnitude scale, which express the size of the quake. Modern seismometers can be incredibly sensitive, capable of detecting even the slightest ground movements. This information is vital for assessing the impact of earthquakes and improving building designs to withstand seismic activity.